Re #8573. Avoid a crash by recursing up the tree if necessary.

Rather than just assuming it's the top level that's selected.
Re #8573. Avoid a bunch of warnings while typing algorithm name.

Just ask the algorithm factory if the algorithm exists rather than trying
to create it on every keystroke (which as well as being expensive gave
a warning log message until the algorithm name was complete).
Merge remote branch 'origin/bugfix/8573_sendto_crash'